The light-emitting diode (LED) is a solid state semiconductor device, which has been broadly used as a light-emitting device. The light-emitting device structure comprises a p-type semiconductor layer, an n-type semiconductor layer, and an active layer. The active layer is formed between the p-type semiconductor layer and the n-type semiconductor layer. The structure of the light-emitting device generally comprises III-V group compound semiconductor such as gallium phosphide, gallium arsenide, or gallium nitride. The light-emitting principle of the LED is the transformation of electrical energy to optical energy by applying electrical current to the p-n junction to generate electrons and holes. Then, the LED emits light when the electrons and the holes combine.
FIG. 1A illustrates a conventional light-emitting device 1a. The light-emitting device 1a comprises a substrate 15a; a semiconductor stack 10a comprising a first type semiconductor layer 13a, a second type semiconductor layer 11a and an active layer 12a formed between the first type semiconductor layer 13a and the second type semiconductor layer 11a; a first electrode 18a electrically connected to the first type semiconductor layer 13a; and a second electrode 19a electrically connected to the second type semiconductor layer 11a. The material of the first electrode 18a and the second electrode 19a comprises metal or metal alloy. As illustrated in FIG. 1A, the first electrode 18a is formed on a top surface 17a of the light-emitting device 1a. The electrical current from the first electrode 18a is not dispersed uniformly in the first type semiconductor layer 13a of the light-emitting device 1a. 
FIG. 1B illustrates another example of a conventional light-emitting device 1b. The light-emitting device 1b comprises a substrate 15b; a semiconductor stack 10b comprising a first type semiconductor layer 13b, a second type semiconductor layer 11b and an active layer 12b formed between the first type semiconductor layer 13b and the second type semiconductor layer 11b; a first electrode 18b electrically connected to the first type semiconductor layer 13b; a second electrode 19b electrically connected to the second type semiconductor layer 11b; and a conductive layer 16b formed between the first type semiconductor layer 13b and the first electrode 18b. The material of the first electrode 18b and the second electrode 19b comprises metal or metal alloy.
As illustrated in FIG. 1B, the conductive layer 16b is formed on the first type semiconductor layer 13b and the first electrode 18b is formed on a top surface 17b of the conductive layer 16b. The material of the conductive layer 16b comprises thin metal or metal alloy. The conductive layer 16b is used to improve the electrical current spreading. However, the transmittance of the conductive layer 16b is low, and the light emitting efficiency of the light-emitting device 1b is affected.